The first thing you need is a good audio interface. I use a Roland UA-4x USB with an AKG studio condenser microphone and put the signal through a TC Helicon pitch corrector.

Use earphones to monitor to prevent feedback from studio monitors.

Record at a level of no more than -6db--bad digital is bad forever.

Use a wav editor like Adobe Audition, WavLab, or Powertracks to duplicate your vocal track. (Or if you can find an old copy of Cool Edit Pro--it is still the best wav editor ever made)

Use the compression effect on each track (it makes the vocal stand out).

Use a slight delay on the duplicate doubled track (makes it stand out more).

Be very cautious using any reverb or room simulations--they are best on the mixed track in most cases.

Powertracks also has the TC Helicon software harmonizer that comes with it--Real Band doesn't. It is actually better than the more expensive stand alone Antares. If you don't have Powertracks get it--best deal in audio.

You need one midi track of the chord progression to make the harmonizer work--it does not have to sound--it just tells the harmonizer what to harmonize.